Biodegradable polymer materials are used in a wide variety of applications, including medical materials, drug delivery systems, and environmentally compatible materials. In recent years, in addition to those applications, there is a need for the biodegradable polymer materials with new functions, and hence, various studies have been conducted. In particular, the introduction of a chemically modifiable functional group into a molecule of a polyhydroxyalkanoate typified by polylactic acid has been examined. There has been reported a compound into which a carboxyl group or a vinyl group is introduced. For example, polymalic acid has been known as a polyhydroxyalkanoate having a carboxyl group at a side chain thereof. An α-type represented by the chemical formula (39) and a β-type represented by the chemical formula (40) have been known as polymers of polymalic acid depending on the form of a polymer.
Of those, a polymer obtained by ring-opening polymerization of a benzyl ester of β-malolactone represented by the chemical formula (41) is disclosed in U.S. Pat. No. 4,265,247 (Patent Document 1) as β-type polymalic acid or a copolymer thereof.
(R41: benzyl group.)
In addition, a polymer obtained by copolymerization of a six-membered ring diester monomer represented by the chemical formula (42) and a glicolide or lactide as a cyclic diester or a lactone as an intramolecular ring closure reaction ester of ω-hydroxycarboxylic acid is disclosed in JP-A 02-3415 (Patent Document 2) as a copolymer containing any one of other hydroxyalkanoic acids typified by α-type polymalic acid-glycolic acid copolymer and glycolic acid.
(R42 represents a lower alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, or a t-butyl group, or a benzyl group.)
Macromolecules 2000, 33 (13), 4619-4627 (Non-Patent Document 1) discloses that 7-oxo-4-oxepanonecarboxylate is subjected to ring-opening polymerization to produce a polymer having an ester group at a side chain thereof, and the polymer is further subjected to hydrogenolysis to produce a polymer having a carboxylic acid at a side chain thereof as a polyhydroxyalkanoate having a carboxyl group at a side chain thereof. Biomacromolecules 2000, 1, 275 (Non-Patent Document 2) discloses a polymer in which a benzyloxycarbonyl group is introduced into a methylene group at α-position of a carbonyl group in the main chain of poly(ε-caprolactone), the polymer being obtained by: allowing lithium diisopropylamide to react with poly(ε-caprolactone); and allowing the resultant to react with benzyl chloroformate. Macromolecular Bioscience 2004, 4, 232 (Non-Patent Document 3) discloses a polymer in which a (benzyloxycarbonyl)methyl group is introduced into a methylene group at α-position of a carbonyl group in the main chain of polylactic acid, the polymer being obtained by: allowing lithium diisopropylamide to react with polylactic acid; and allowing the resultant to react with benzyl bromoacetate.
Polymeric Materials Science & Engineering 2002, 87, 254 (Non-Patent Document 4) discloses, as a polyhydroxyalkanoate having a vinyl group at a side chain thereof, a polymer obtained by ring-opening polymerization of α-allyl(δ-valerolactone). Similarly, Polymer Preprints 2002, 43 (2), 727 (Non-Patent Document 5) discloses, as a polyhydroxyalkanoate having a vinyl group at a side chain thereof, a polymer obtained by ring-opening polymerization of 3,6-diallyl-1,4-dioxane-2,5-dione as a six-membered ring diester monomer.
There has been reported a polymer having a new function into which a structure providing functional properties for a polyhydroxyalkanoate into which a chemically modifiable functional group is introduced as described above is introduced. International Journal of Biological Macromolecules 25 (1999) 265 (Non-Patent Document 6) discloses the following. A copolymer of α-type malic acid and glycolic acid is obtained by ring-opening polymerization of a cyclic dimer of α-type malic acid and glycolic acid, and the resultant polymer is deprotected to obtain a polyester having a carboxyl group at a side chain thereof. Tripeptide is chemically modified to the carboxyl group at the side chain, and the resultant polymer is evaluated for cell adhesion. At this time, a good result is obtained.